High-resolution, in situ structures of the blood-brain barrier and neurovascular disease

Context: Historically structural biology experiments have been conducted on proteins ‘grown’ in the lab and although they provided some key insights in understanding molecular mechanisms and for developing leads to therapeutic development, it has become clear that the structure and activity of proteins is influenced by their native cellular context. Therefore, it is essential that moving forwards we study these systems in tissue. To this end we have in the past year published the first structure of a protein within human brain. Challenge: In 2022, dementia and cerebrovascular disease were the first and third most prevalent causes of death in the UK, respectively (ONS). The neurovascular unit that forms the blood brain barrier (BBB) is a strictly controlled gateway mediating entry of essential nutrients and the removal of waste and toxins, including ß-amyloid. The BBB is a particular challenge for pharmaceuticals targeted to the brain because it also limits the uptake of therapeutics. For example, the MHRA and FDA recently approved an Alzheimer’s disease (AD) immunotherapy for which less than 1% of the dose crosses the BBB. This increases cost and likely contributes to unwanted inflammation at the BBB that can result in fatal side-effects of the treatment. Cerebral amyloid angiopathy (CAA) is an incurable disease in which amyloid accumulates at the BBB and is also a co-pathology in ~50% of AD cases, likely increasing the risk of therapeutic side effects. Aims: This project will use multiple imaging modalities (cryoEM/cryoET, cryoFIB-SEM ‘mill and view’ and cryo-fluorescence) to determine molecular structure, 3D molecular architecture, and cellular-resolution tissue maps of the neurovascular unit in human brain tissue (postmortem and living donor): Determine the first in-tissue structure of vascular amyloid. The first 3D molecular architecture and cellular-resolution model of the neurovascular unit in postmortem vascular disease and living donor fresh brain tissue. Obtain the first in-tissue cryoET molecular architecture of vascular amyloid engaged with an Alzheimer’s disease immunotherapeutic. Potential applications and impacts: Knowledge of the in-tissue structure of vascular amyloid could contribute to the long-term effort to develop vascular amyloid-specific ligands for diagnostics (eg. CAA-specific PET ligands) and/or therapeutics to prevent cerebral amyloid angiopathy. What is the impact of a structural model of the neurovascular unit bridging both molecular and cellular length-scales in human brain? Being able to relate directly the structure of proteins, their molecular architecture within 3D cellular resolution tissue maps of vascular disease will impact our understanding CAA and AD. Since BBB permissiveness is a major challenge in treating many other neurological diseases, including brain tumours and mental health, this structural blueprint will likely aid the design of therapeutics that must cross the BBB and drug delivery technologies that are currently in development. More broadly, this discovery project will further develop physical/structural technology imaging across space (patients to molecules) and time (from health to disease) to accelerate our understanding of disease and the development of immunotherapeutics.